1. Field of the Invention
The invention relates to an apparatus for cutting pipe in a borehole extending into the earth from the surface.
2. Description of the Prior Art
U.S. Pat. Nos. 4,298,063, 4,598,769, 5,435,394, and 6,186,226B1 disclose apparatus for cutting pipe in a borehole. U.S. Pat. Nos. 4,598,769 and 5,435,394 are incorporated into the application by reference. In U.S. Pat. Nos. 4,598,769 and 5,435,394, the apparatus comprises an elongated body to be located in the pipe. The body has a central opening extending between an upper ignition device and a lower nozzle. Solid combustible material is located in the opening. The nozzle has a plurality of spaced apart apertures extending therethrough angularly around the axis leading to a diverter. The diverter has a flared surface which curves outward from a small circumference near the nozzle to an enlarged annular circumference. In operation, the ignition device is actuated to ignite the combustible material to form a flame of hot gases for passage through the apertures of the nozzle to the curved surface. The surface directs the flame and hot gases radially outward, which moves a sleeve down and the flame outward against the pipe for severing purposes.
Although the apparatus severs a pipe, sometimes problems occur in that the apertures of the nozzle become clogged and/or the severing procedure is not uniform due to the concentration of heat points of the flame radially outward from the exits of the apertures of the nozzle.
It is an object of the invention to provide an apparatus which is an improvement to the apparatus of U.S. Pat. Nos. 4,598,769, and 5,435,394 in that it avoids the problems mentioned above.
The apparatus of this invention comprises a uniform mixing cavity above the nozzle in the flow path of the flame to the nozzle which allows the hot gases to mix and provides a more even distribution of the hot gases through the nozzle apertures to prevent the nozzle apertures from being plugged.
The invention also provides a lower mixing cavity for the hot gases flowing out of the nozzle which pressurizes the annular gap at the outlet of the curved surface of the diverter and more evenly distributes the outward flowing hot gases around the curved surface of the diverter to obtain a move even cutting of the pipe around its circumference.